1. Field of the Invention
The present invention relates to a tower crane and, more particularly, to mechanism on the tower for supporting the load.
2. Description of the Prior Art
In a tower crane, it is convenient to have the boom, which is supported by the tower, foldable down along the front of the tower for dismantling and/or transport. To accomplish this, it is common to pivotally mount the boom on the front edge of the tower, as shown, for example, in U.S. Pat. Nos. 3,134,488; 3,246,769; 3,252,585; 3,767,061; 3,804,264; 3,844,418; 3,856,160; 3,300,361. Pivotally connecting the load-carrying boom, however, to the front edge of the tower produces an eccentric loading on the tower. Such an eccentric loading on the tower limits the magnitude of the load which can be handled by the boom.
There have, in the past, been tower cranes with a boom foldable along the front edge of the tower in which eccentric loading of the tower was avoided. For example, in U.S. Pat. No. 3,794,184, the boom is pivotally connected centrally of a plate which is connected to the top of the tower boom to center the load of the boom on the tower. The plate, however, can be pivoted about the front edge of the tower to permit the boom to be lowered. Another example of a tower crane in which a centrally mounted boom on the tower can be folded along the front edge of the tower is shown in U.S. Pat. No. 3,433,368. In this crane, the boom has a laterally extending foot extension which is pivotally connected at the top of the tower between the front and rear edges of the tower.